The present invention relates to industrial furnaces in general, and more particularly to improvements in grates which can be used in such types of furnaces. Still more particularly, the invention relates to improvements in grates of the type wherein mobile grate bars alternate with stationary grate bars and the mobile grate bars are coupled to but can be displaced relative to the adjacent stationary grate bars.
Grates of the above outlined character are equipped with means for moving the mobile grate bars relative to the stationary grate bars. Reference may be had to U.S. Pat. No. 4,239,029 wherein FIG. 2 shows a portion of a grate with mechanically movable bars. The ribs at the underside of the mobile grate bar which is shown in FIG. 2 are provided with elongated slots for portions of a coupling device which secures the neighboring stationary grate bars to each other but enables the mobile grate bar between the stationary bars to perform requisite movements with reference thereto. The coupling device is a one-piece body having an elongated central portion or stem extending through the slots of ribs at the underside of the mobile bar and two enlarged end portions which abut against the adjacent surfaces of ribs at the undersides of the neighboring stationary bars and hold such stationary bars against movement away from each other, i.e., away from the respective sides of the mobile bar. The end portions of the coupling device have flat surfaces which are in full contact with the adjacent surfaces of the corresponding stationary bars. A drawback of this coupling device is that it is likely to jam and to thus prevent the mobile bar from moving forwardly and backwards with reference to the stationary bars. Moreover, particles of partially combusted solid fuel and/or cinder which penetrate between the stationary and mobile grate bars invariably tend to subject the coupling device to eccentric forces which entail a flexing of the coupling device and even permanent bending which evidently interferes with predictable movements of the mobile grate bar relative to the neighboring stationary bars.
Another drawback of the just discussed conventional coupling device is that it cannot be adequately adjusted to compensate for progressing wear upon the grate bars. The wear is quite extensive and, therefore, the distance between the stationary grate bars which flank the mobile bar will increase considerably as the wear progresses. Adjustability is further desirable on the grond that, when one or more grate bars require a secondary treatment after a certain period of use, such secondary treatment normally entails removal of at least some material with resulting further increase in tolerances which cannot be compensated for by the just described conventional coupling device. As a rule, wear is compensated for by removing a previously employed coupling device and replacing it with a fresh coupling device.
FIG. 4 of the aforementioned patent discloses a screw which is provided to facilitate adjustment of the coupling device relative to the grate bars in order to compensate for wear and manufacturing tolerances. Such one-sided adjustment is unsatisfactory and insufficient when the wear is pronounced and/or upon completion of secondary treatment of one or more grate bars. Still further, the single screw tends to urge the other end portion of the coupling device flush against the adjacent surface of the corresponding stationary grate bar.
FIG. 8 of the aforementioned patent discloses a coupling device with two transversely extending screws. A drawback of such proposal is that the extent of adjustability is minimal and also that the two screws must be carefully adjusted to the same extent in order to ensure balanced distribution of stresses. Also, the screws tend to become loose when the grate is in use so that the reliability of the coupling device is questionable.
A drawback which is common to all embodiments of the patented grate is that a defective grate bar can be removed only upon removal or shifting of several coupling devices. This is a time-consuming operation which contributes significantly to the down times of the grate and of the entire furnace.